THE ACTION OF FROST. IN WATER-PIPES. 33 



\vhich is perfectly cylindrical other conditions equal will be 

 less likely to burst than one which is of varying diameter, as 

 the sliding from a larger to a smaller portion of the pipe must 

 be attended with great resistance, or a certain degree of block, 

 beyond what would be due to the mere friction along a pipe 

 of uniform diameter. 



Let us now consider the relative merits of lead and iroa as 

 material for water-pipes in places where exposure to frost is 

 inevitable. Lead yields more than iron, and so far has an 

 advantage ; this, however, is but limited. As lead is practi- 

 cally inelastic, every stretch remains, and every stretch di- 

 minishes the capacity for further stretching ; the lead thus 

 stretched at one frost is less able to stretch again, and has 

 lost some of its original tenacity. Hence the superiority of 

 new leaden pipes. Iron is elastic within certain limits, and 

 thus the iron pipe may yield a little without permanent strain 

 or " distress," and if its power of elastic resistance is not 

 exceeded, it regains its original size without becoming sensibly 

 weaker. Add to this its great tenacity, its non-liability to be 

 indented, or otherwise to vary in diameter, and we have a far 

 superior material. 



But this conclusion demands some qualification. There is 

 iron and iron, cast iron and wrought iron, and very variable 

 qualities of each of these. I need scarcely add that common 

 brittle cast iron is quite out of the question for such purposes, 

 though there is a new kind of cast iron or semi-steel coming 

 forward that may possibly supersede all other kinds ; but this 

 opens too wide a subject for discussion in the present paper, 

 the main object of which has been a popular exposition of the 

 general physical laws which must, be obeyed by the builder, 

 or engineer, who desires to construct domestic or other build- 

 ings that will satisfy the wants of intelligent people. 



The mischievous action of freezing water is not confined to 

 the pipes that are constructed to receive or convey it. Wher- 

 ever water may be, if that water freezes, it must expand in the 

 degree and with the force already described. If it penetrates 

 stone or brick, or mortar or stucco, and freezes therein, one of 

 two things must occur either the superfluous ice must exude 

 at the surface or to neighboring cavities, or the saturated 

 material must give way, and split or crumble according to the 

 manner and degree of penetration. To understand this, _the 

 reader must remember what I stated about the little-understood 

 viscosity of ice, as well as its expansion at the moment of freezing. 



